Backing and adhesives must be chosen with care, as may be visible through glass.

Mirror glass can be very effective but splinters when cut so take care.

Clear glass with foiled or painted backing also available but more expensive than vitreous glass.

Easy to cut

Shells:

Cheap.

Fun to collect.

Frost-hardy.

Too porous to be grouted in the normal way, as they will stain.

Found objects:

Many found objects can be incorporated into a mosaic if you wish ­ metal, plastic, stone, even teeth! ­ if they are stuck down firmly.

Backing materials

If you browse through books or web sites you'll see that virtually any object can be mosaicked. The most commonly used backing is wood. This should be of a kind that will not warp, for example a fibre board (such as MDF) or plywood. If it will go out of doors, an exterior grade wood should be chosen. The back of a tile can be used very successfully as a mosaic base, as it is porous and gives very good adhesion.

It is usual to prepare wooden surfaces by priming and scoring them. Priming involves painting on a coat of diluted PVA glue (about one part glue to 5-10 parts water). This seals the surface, meaning that glue and grout will not dry too quickly. Scoring lines with a craft knife or Stanley knife makes the surface rougher, giving a better grip.

Adhesives

Choice of adhesive is important. For most purposes, PVA (Poly Vinyl Acetate) glue is ideal (also known as "white craft glue"). This is widely available. Generally the most cost-effective way of buying it is in quantity from a builders' merchant. It is fairly quick drying (within several hours), moderately water-resistant when dry, and relatively low hazard.

Household tile adhesive: Good "grab" for 3-D projects. Useful where the tesserae are not flat, as it can fill the space behind. Generally relatively low hazard.

Epoxy resin: Very strong. Fast setting versions available. Good for non-porous contacts e.g. with metal, or where quick repairs needed. High hazard, not pleasant to use.

Bathroom sealant: Very effective for ceramic-to-ceramic bonds. High "grab", so good for 3-D work. Can work out relatively costly.